A slightly more acidic ocean may help coral species

Justin Ries, an associate professor at the Marine Science Center, researches biogeochemical oceanic change over long time periods. Photo by Brooks Canaday

Researchers from North­eastern University’s Marine Sci­ence Center and the Uni­ver­sity of North Car­olina at Chapel Hill have found that mod­erate ocean acid­i­fi­ca­tion and warming can actu­ally enhance the growth rate of one reef-​​building coral species. Only under extreme acid­i­fi­ca­tion and thermal con­di­tions did cal­ci­fi­ca­tion decline.

Justin Ries, an asso­ciate pro­fessor at North­eastern and one of the paper’s co-​​authors, focuses his research on the bio­log­ical impacts of rising atmos­pheric carbon dioxide levels, which has been increasing ocean acidity since the Indus­trial Rev­o­lu­tion. One group of organ­isms that would be greatly affected by ocean acid­i­fi­ca­tion are those that build cal­cium car­bonate shells and skele­tons, such as coral, snails, and clams, which, he said, are already near the point of dis­solving in some parts of the ocean.

The authors attribute the coral’s pos­i­tive response to mod­er­ately ele­vated carbon dioxide to the fer­til­iza­tion of pho­to­syn­thesis within the coral’s algal sym­bionts, which may pro­vide the coral with more energy for cal­ci­fi­ca­tion even though the sea­water is more acidic. They pro­pose that the even­tual decline in coral cal­ci­fi­ca­tion at the very high levels of carbon dioxide occurs when the ben­e­fi­cial effects of fer­til­izing pho­to­syn­thesis are out­weighed by the neg­a­tive effects of acid­i­fi­ca­tion on the skeleton-​​forming process.

“The study showed that this species of coral (Sideras­trea siderea) exhib­ited a peaked or par­a­bolic response to both warming and acid­i­fi­ca­tion, that is, mod­erate acid­i­fi­ca­tion and warming actu­ally enhanced coral cal­ci­fi­ca­tion, with only extreme warming and acid­i­fi­ca­tion neg­a­tively impacting the corals,” Ries said. “This was sur­prising given that most studies have shown that corals exhibit a more neg­a­tive response to even mod­erate acidification.”

Fur­ther­more, their work indi­cates that ocean warming is likely to threaten this coral species more than acid­i­fi­ca­tion by the end of the cen­tury, based on pro­jec­tions from the Inter­gov­ern­mental Panel on Cli­mate Change.

He noted that in the past 200 years, ocean pH level has dropped from 8.2 to 8.1 and is expected to fall even fur­ther to about 7.8 over the next one or two cen­turies. That is a sig­nif­i­cant decrease over a rel­a­tively short period of time, Ries said, when looking at the geo­logic his­tory of ocean acidification.

“The amount of change that would typ­i­cally occur in about 10 mil­lion years is being con­densed into a 300-​​year period,” Ries said. “It’s not the just the mag­ni­tude of the change that mat­ters to the organ­isms, but how quickly it is occurring.”

In addi­tion to pub­lishing these find­ings, Ries has lever­aged his research in this area to secure a pres­ti­gious fel­low­ship from the Hanse Wis­senschaft­skolleg Insti­tute for Advanced Study in Del­men­horst, Ger­many and a sup­porting research award from the National Sci­ence Foun­da­tion. He will spend 10 months over the next four years there working with researchers at three promi­nent German research insti­tu­tions to use var­ious tools such as micro­elec­trodes, iso­tope ratios, and pH sen­si­tive dyes to see how ocean acid­i­fi­ca­tion affects the organ­isms’ internal cal­ci­fying processes that lead to the for­ma­tion of their shells and skeletons.

“Acid­i­fi­ca­tion of the sur­rounding sea­water is cer­tainly impor­tant for marine organ­isms, but what is equally as impor­tant — per­haps even more impor­tant — is how the chem­istry of their internal cal­ci­fying fluid responds to these changes in sea­water chem­istry,” Ries said.

About the Writer

Joe O'Connell is a staff writer for News@Northeastern. A former newspaper reporter and editor, Joe came to Northeastern after working for three different daily newspapers in Massachusetts. Joe is a UNH grad and is finding it difficult to pick which hockey team to cheer for. When he isn't working, Joe can be found watching Boston's sports teams in their athletic endeavors, playing golf badly, and washing hospital scrubs. Follow him on Twitter @joconnell_nu

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